A Harvard astrophysicist who proposed that a puzzling object racing through the solar system may be a missing Soviet spacecraft is challenging NASA Administrator Jared Isaacman’s assessment that it is simply an asteroid.
The object, known as 1998 KY26, measures about 36 feet across and is generally classified as a near-Earth asteroid. However, its apparent acceleration cannot be fully explained by gravity. Harvard astrophysicist Avi Loeb and his colleagues have explored whether KY26 could instead be Phobos 1, a Soviet probe that lost contact with Earth while en route to Mars in 1988.
Isaacman addressed the unusual object Thursday during an appearance on “Fox & Friends.”
“I’ve not seen any evidence to suggest this is…anything other than an asteroid,” Isaacman said.
Two shape models depict scientists’ estimates for the appearance of near-Earth object 1998 KY26. (Credit: NASA)
Loeb disputed that conclusion in a Friday interview with News Outlet.
“Well, first of all, it’s not an asteroid because 1998 KY26 appears to have non-gravitational acceleration, meaning it’s being pushed by some force other than gravity, and asteroids are just rocks,” Loeb said.
Researchers have been searching for an explanation for the object’s unexplained acceleration.
One possibility is that KY26 is a “dark comet”—a rocky body that acts like a comet but shows no obvious cloud or tail.
An illustration depicts the Soviet Phobos 1 spacecraft, launched toward Mars in July 1988 before a faulty command caused it to shut down and contact was lost. (Credit: NASA)
Research from Georgia Tech has questioned whether KY26 could preserve enough ice to create such an effect. Other studies, meanwhile, suggest that sunlight pressure and heat radiating from the object’s surface could explain the acceleration.
Loeb said his team found that KY26’s path closely matches the trajectory expected for the failed Soviet mission. The researchers also calculated that sunlight reflecting from Phobos 1 could generate a force consistent with the non-gravitational acceleration detected in KY26.
He further cited observations suggesting that the object is unusually reflective and completes a rotation roughly every five minutes.
A model of Phobos 1, the Soviet probe that lost contact with Earth while traveling to Mars in 1988. Avi Loeb and his colleagues are investigating whether 1998 KY26 could be the missing spacecraft. (Credit: NASA)
For Loeb, the absence of a visible tail or escaping material is a major problem for the dark-comet theory.
“It could be a comet shedding some gas backward that is pushing it forward, but in that case we should have seen the gas,” Loeb said. “We should have seen the dust because for comets we see a tail and the dust particles are being pushed away from the sun by the solar radiation.”
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“We don’t see a cometary tail. We don’t see any evidence for outgassing around this object. That’s the puzzle,” he added.
Loeb likened the disagreement over KY26’s identity to finding an unfamiliar animal in a zoo.
Avi Loeb speaks at the SALT conference in Manhattan, New York City, on September 14, 2022. (David ‘Dee’ Delgado)
“If you are an expert on zebras and you see an elephant, you would say the elephant is a zebra without stripes,” Loeb said. “But that’s an oxymoron because it’s a completely different animal.”
He said scientists should remain open to possibilities beyond the standard asteroid and comet categories when an object’s behavior does not fit either classification.
“Innovation in science requires some imagination,” Loeb said. “It requires you to allow for the possibility that our knowledge is incomplete.”
News Outlet contacted NASA for a response to Loeb’s claims and asked whether Isaacman continues to stand by his assessment of KY26.
Jared Isaacman, President Donald Trump’s nominee to lead the National Aeronautics and Space Administration, testifies during a Senate Commerce, Science and Transportation Committee confirmation hearing at the Russell Senate Office Building on Capitol Hill on April 9, 2025, in Washington. (Kevin Dietsch/Getty Images)
Loeb conceded that his team’s explanation has not been proven. However, he said the mystery could be resolved in 2031, when the Japan Aerospace Exploration Agency’s Hayabusa2 spacecraft is expected to rendezvous with KY26.
He believes the encounter could reveal that researchers have been tracking a remnant of Soviet space history rather than an unusual natural body.
A concept illustration shows an asteroid passing near Earth. (iStock)
“We predict that when they land on it, instead of seeing an iceberg, they will find the label ‘Made in the USSR,’” Loeb said.
Loeb also said the Hayabusa2 encounter could definitively resolve the debate.
When asked whether the Phobos 1 theory would be disproved if Hayabusa2 reaches KY26 and finds a rock or ice, Loeb answered without hesitation.
“Yes,” he said.
